The invention relates to an electro-optical liquid-crystal display having a realignment layer for realignment of the liquid crystals whose field has a component, which aids the realignment, parallel to the liquid-crystal layer, containing a liquid-crystalline medium of positive dielectric anisotropy, where the medium comprises at least one mesogenic compound of the formula I: 
in which
R1 is alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 7 carbon atoms, and
L is H or F.
In conventional liquid-crystal displays (TN, STN, OMI or AMD-TN), the electric fields for realignment are generated essentially perpendicular to the liquid-crystal layer.
International Patent Application WO 91/10936 discloses a liquid-crystal display in which the electric signals are generated in such a way that the electric fields have a significant component parallel to the liquid-crystal layer (IPS, in-plane switching). The principles of operating a display of this type are described, for example, by R. A. Soref in Journal of Applied Physics, Vol. 45, No.12, pp. 5466-5468 (1974).
EP 0 588 568, for example, discloses various possibilities for the design of the electrodes and for addressing a display of this type. DE 198 24 137 likewise describes various embodiments of IPS displays of this type.
Liquid-crystalline materials for IPS displays of this type are described, for example, in DE 195 28 104.
The IPS displays containing the known liquid-crystalline media are characterized by inadequate, long response times and often excessively high operating voltages. There is thus a demand for IPS displays which do not have these disadvantages or only do so to a reduced extent. To this end, liquid-crystalline materials are required which, besides an adequate phase range, low tendency towards crystallization at low temperatures, low birefringence and adequate electrical resistance, have, in particular, low threshold voltages (V10) and low rotational viscosities (xcex31), which are crucial for the response times.
This feature has, surprisingly, been achieved by the use of liquid-crystalline materials which comprise at least one compound of the formula I.
The IPS mixtures according to the invention are distinguished by their relatively low rotational viscosity values and their low threshold voltage and response time values.
The invention thus relates to an electro-optical liquid-crystal display having a realignment layer for realignment of the liquid crystals whose field, desirably, has a significant component parallel to the liquid-crystal layer, containing a liquid-crystalline medium of positive dielectric anisotropy, where the medium comprises at least one compound of the formula I: 
in which
R1 is alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 7 carbon atoms, and
L is H or F.
Particular preference is given to compounds of the formula I in which L is F, and to compounds of the formula I in which R1 is alkyl or alkoxy having 1 to 7 carbon atoms.
The compounds of the formula I have high dielectric anisotropy values and relatively high birefringence and clearing point values. Their use in liquid-crystal mixtures for IPS displays according to the invention facilitates high dielectric anisotropies and low rotational viscosities with retention of high clearing points and favourable birefringence values and produces low threshold voltages and short response times.
It has been found, in particular, that mixtures according to the invention comprising compounds of the formula I have significantly higher clearing point and dielectric anisotropy values, lower rotational viscosity and threshold voltage values, and shorter response times than, for example, analogous mixtures which, instead of the compounds of the formula I, comprise 3,5-difluoro-4-cyanophenylcyclohexanes of the formula: 
The compounds of the formula I are disclosed in DE 44 10 606. However, this specification does not describe IPS displays.
Preferred embodiments are IPS displays in which
a) the liquid-crystalline medium comprises one or more compounds of the formula II containing a cyano group: 
in which
R2 is H, an alkyl or alkenyl radical having 1 to 15 carbon atoms which is unsubstituted, monosubstituted by CN or CF3 or at least monosubstituted by halogen, where one or more CH2 groups in these radicals may also each, independently of one another, be replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94 or xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94 in such a way that O atoms are not linked directly to one another,
A1 and A2 are each, independently of one another,
(a) a trans-1,4-cyclohexylene radical or 1,4-cyclohexenylene radical, in which, in addition, one or more non-adjacent CH2 groups may be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94Sxe2x80x94,
(b) a 1,4-phenylene radical, in which, in addition, one or two CH groups may be replaced by N,
(c) a radical from the group consisting of 1,4-bicyclo-[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl,
where the radicals (a) and (b) may be substituted by one or two fluorine atoms,
Z1 and Z2 are each, independently of one another, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94CHFxe2x80x94CHFxe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94CF2CF2xe2x80x94 or a single bond, and one of the radicals Z1 and Z2 may alternatively be xe2x80x94(CH2)4xe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94CH2CH2xe2x80x94,
L1 and L2 are each, independently of one another, H or F; and
m is 0, 1 or 2;
b) the liquid-crystalline medium comprises one or more compounds of the formula III containing a 3,4,5-trifluorophenyl group: 
in which
R3 has one of the meanings indicated for R2 in the formula II,
A3 and A4 each, independently of one another, have one of the meanings indicated for A1 and A2 in the formula II,
Z3 and Z4 each, independently of one another, have one of the meanings indicated for Z1 and Z2 in the formula II, and
n is 0, 1 or 2;
c) the liquid-crystalline medium comprises one or more compounds of the formula IV:
R4xe2x80x94(A5xe2x80x94Z5)oxe2x80x94A6xe2x80x94R5xe2x80x83xe2x80x83IV
in which
R4 and R5 each, independently of one another, have one of the meanings indicated for R2 in the formula II,
A5 and A6 each, independently of one another, have one of the meanings indicated for A1 and A2 in the formula II,
each Z5, independently of the others, has one of the meanings indicated for Z1 and Z2 in the formula II, and
o is 1, 2 or 3;
d) the liquid-crystalline medium comprises one or more compounds of the formula V: 
in which
R6 has one of the meanings indicated for R2 in the formula II,
A7 and A8 each, independently of one another, have one of the meanings indicated for A1 and A2 in the formula II,
Z7 and Z8 each, independently of one another, have one of the meanings indicated for Z1 and Z2 in the formula II,
L1 and L2 are each, independently of one another, H or F,
Q is a polyfluoroalkylene radical of the formula
xe2x80x94(O)qxe2x80x94(CH2)rxe2x80x94(CF2)sxe2x80x94, in which
q is 0 or 1,
r is 0, 1, 2, 3, 4, 5 or 6,and
s is 1, 2, 3, 4, 5 or 6,
X is H, F or Cl, and
p is 0, 1 or 2.
The compounds of the formula II are preferably selected from the group comprising the formulae IIa to IIp: 
in which R2 is as defined in the formula II, and L2 is H or F.
In the compounds of the formulae IIb, IIe, IIk, IIn and IIp, L2 is particularly preferably F. In the compounds of the formulae IId, IIg, IIh and IIi, L2 is particularly preferably H.
The liquid-crystalline medium particularly preferably comprises one or more compounds selected from the group consisting of the compounds of the formulae IIa, IIb, IIc, IId, IIh and IIk.
In a further preferred embodiment, the liquid-crystalline medium comprises at least one heterocyclic compound selected from the group comprising the formulae IIm, IIn, IIo and IIp.
The compounds of the formula III are preferably selected from the group comprising the formulae IIIa to IIIi: 
in which R3 is as defined in the formula III.
The liquid-crystal display particularly preferably contains a liquid-crystalline medium comprising one or more compounds selected from the group comprising the formulae IIIc, IIId, IIIe, IIIf, IIIg, IIIh, IIIi, IIIk and IIIn.
The compounds of the formula IV are preferably selected from the group comprising the formulae IVa to IVm: 
in which R4 and R5 are as defined in the formula IV, and L is H or F.
In the compounds of the formula IVk, L is particularly preferably F.
The liquid-crystal display particularly preferably contains a liquid-crystalline medium comprising one or more compounds selected from the group consisting of the compounds of the formulae IVb, IVe, IVk and IVm.
The compounds of the formula V are preferably selected from the group comprising the formulae Va to Vi: 
in which R6 is as defined in the formula V, and L is H or F.
In the compounds of the formula Vd, L2 is particularly preferably F.
The liquid-crystalline medium particularly preferably contains one or more compounds selected from the group consisting of the compounds of the formulae Va, Vc, Vd, Ve and Vf.
In a further preferred embodiment, the liquid-crystalline medium comprises one or more alkenyl compounds of the formula VI: 
in which
R7 is an alkenyl group having 2 to 7 carbon atoms,
Z9 is xe2x80x94CHxe2x95x90CHxe2x80x94 or a single bond,
L is H or F,
a is 0 or 1, and
R8 is an alkyl, alkoxy or alkenyl group having 1 to 12 carbon atoms, in which, in addition, one or two non-adjacent CH2 groups may be replaced by xe2x80x94Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94OCOxe2x80x94 or xe2x80x94COOxe2x80x94 in such a way that O atoms are not linked directly to one another, or, if a is 1, is alternatively F.
The compounds of the formula VI are preferably selected from the group comprising the formulae VIa to VIf: 
in which
k is 1, 2, 3, 4 or 5,
m and n are each, independently of one another, 0, 1, 2 or 3, where m+n is xe2x89xa65, and
o is 0 or 1.
In the compounds of the formula IIIf, L is preferably F.
Further preferred embodiments are the following IPS displays:
the medium additionally comprises one or more compounds containing a 4-fluorophenyl group, selected from the group consisting of the formulae VIIa to VIIc: 
xe2x80x83in which R9 has the one of the meanings indicated for R3 in the formula III, and in particular is alkyl having 1 to 7 carbon atoms;
the medium additionally comprises one or more compounds of the formula VIII: 
xe2x80x83in which R10 and R11 are each, independently of one another, alkyl or alkoxy, preferably alkyl, having 1 to 7 carbon atoms;
the medium additionally comprises one or more compounds of the formula IX: 
the medium additionally comprises one or more compounds of negative dielectric anisotropy selected from the group consisting of the formulae X and XI: 
xe2x80x83in which R12 and R13 are each, independently of one another, alkyl or alkoxy having 1 to 7 carbon atoms, R12 is preferably alkyl, R13 is preferably alkoxy.
Preference is given to displays containing liquid-crystal mixtures comprising
one or more cyano compounds selected from the group comprising the formulae IIa, IIb, IId, IIg and IIk, in particular compounds of the formulae IIb, IIg and IIk in which L2 is F, and compounds of the formula IId in which L2 is H,
one or more dioxane compounds selected from the group comprising the formulae IIm and IIn, in particular of the formula IIn in which L2 is F,
one or more 3,4,5-trifluorophenyl compounds selected from the group comprising the formulae IIIc, IIIg and IIIh,
one or more compounds selected from the group comprising the formulae IVb, IVh, IVk and IVm, in which R4 and R5 are preferably straight-chain alkyl having 1 to 7 carbon atoms, in the compounds of the formula IVb R5 is preferably alkoxy having 1 to 5 carbon atoms, and in the compounds of the formula IVk L is preferably F,
one or more compounds selected from the group comprising the formulae Va, Vc and Vg,
one or more alkenyl compounds selected from the group comprising the formulae VIa, VIb, VIe and VIf, where
in the compounds of the formula VIa, preferably m and/or n, particularly preferably m and n, are 0,
in the compounds of the formula VIb, n is preferably 0,
in the compounds of the formula VIe, k is preferably 0,
in the compounds of the formula VIf, L is preferably F, and m and n are preferably 0,
from 2 to 40% by weight, in particular from 3 to 25% by weight, of one or more, preferably one, two or three, compounds of the formula I.
Preference is furthermore given to a liquid-crystal display according to the invention in which the pixels are addressed by means of an active matrix.
The invention furthermore relates to a liquid-crystalline medium of positive dielectric anisotropy comprising at least one compound of the formula I, at least one compound selected from the group consisting of the compounds of the formulae IIa to IIp, IIIa to IIIk and Va to Vi, at least one compound selected from the group consisting of the compounds of the formulae VIa to VIf, and, if desired, one or more compounds selected from the group consisting of the compounds of the formulae IVa to IVm, in particular which comprises
from 2 to 40, preferably from 3 to 30, particularly preferably from 3 to 22% by weight of at least one compound of the formula I,
from 15 to 85, preferably from 20 to 65% by weight of at least one compound selected from the group consisting of the compounds of the formulae II and III,
from 0 to 75, preferably from 10 to 67, particularly preferably from 15 to 40% by weight of at least compound of the formula II,
from 0 to 55, preferably from 5 to 50, particularly preferably from 10 to 40% by weight of at least one compound of the formula III,
from 0 to 60, preferably from 5 to 45% by weight of at least one compound of the formula IV,
from 0 to 40, preferably from 5 to 35, particularly preferably from 10 to 25% by weight of at least one compound of the formula V,
from 0 to 55, preferably from 5 to 45% by weight of at least one compound of the formula VI.
The liquid-crystalline media used in accordance with the invention generally have a birefringence (xcex94n) of  less than 0.14, preferably in the range from 0.06 to 0.13, in particular in the range from 0.09 to 0.12, with clearing points of from 65 to 95xc2x0 C., in particular from 70 to 85xc2x0 C.
The flow viscosity (at 20xc2x0 C.) of the mixtures used in accordance with the invention is generally less than 30 mm2xc2x7sxe2x88x921, in particular between 15 and 25 mm2xc2x7sxe2x88x921. The resistivity of the materials according to the invention is generally, at 20xc2x0 C., from 5xc3x971010 to 5xc3x971013 xcexa9xc2x7cm, particularly preferably from 5xc3x971011 to 5xc3x971012 xcexa9xc2x7cm. The rotational viscosity of the mixtures according to the invention is generally, at 20xc2x0 C., less than 140 mPaxc2x7s, in particular from 80 to 130 mPaxc2x7s.
Media having clearing points of from 70 to 80xc2x0 C. which are used in accordance with the invention have rotational viscosities of 130 mPaxc2x7s or less, preferably from 80 to 120 mPaxc2x7s.
The clearing point of the media used in accordance with the invention is greater than 60xc2x0 C., preferably greater than 70xc2x0 C. and particularly preferably 75xc2x0 C. or greater. In particular, the clearing point is in the range from 60xc2x0 C. to 85xc2x0 C. The shelf life in test cells, determined as described below, is 1000 hours or more at xe2x88x9230xc2x0 C., preferably 500 hours or more at xe2x88x9240xc2x0 C. and very particularly preferably 1000 hours or more at xe2x88x9240xc2x0 C.
The media used in accordance with the invention consist of from 5 to 30 compounds, preferably of from 6 to 20 compounds and particularly preferably of from 7 to 16 compounds.
It has been found that even a relatively low proportion of compounds of the formula I in a mixture with conventional liquid-crystal materials, but in particular with one or more compounds selected from the group consisting of the compounds of the formulae IIa to IIIk and/or from the group consisting of the compounds of the formulae IVa to VIf, results in a significant lowering of the threshold voltage, in favourable rotational viscosity values xcex31 and in fast response times, with, in particular, broad nematic phases with low smectic-nematic transition temperatures being observed. The compounds of the formulae I to VI are colorless, stable and readily miscible with one another and with other liquid-crystal materials.
The term xe2x80x9calkylxe2x80x9d covers straight-chain and branched alkyl groups having 1-7 carbon atoms, in particular the straight-chain groups methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups having 2-5 carbon atoms are preferred, unless explicitly stated otherwise.
The term xe2x80x9calkenylxe2x80x9d covers straight-chain and branched alkenyl groups having 2-7 carbon atoms, in particular the straight-chain groups. Particularly preferred alkenyl groups are C2-C7-1E-alkenyl, C4-C7-3E-alkenyl, C5-C7-4-alkenyl, C6-C7-5-alkenyl and C7-6-alkenyl, in particular C2-C7-1E-alkenyl, C4-C7-3E-alkenyl and C5-C7-4-alkenyl. Examples of very particularly preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3E-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having up to 5 carbon atoms are preferred, unless explicitly stated otherwise.
The term xe2x80x9cfluoroalkylxe2x80x9d preferably covers straight-chain groups having a terminal fluorine, i.e. fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. However, other positions of the fluorine are not excluded.
The term xe2x80x9calkoxyalkylxe2x80x9d preferably covers straight-chain radicals of the formula CnH2n+1xe2x80x94Oxe2x80x94(CH2)m, in which n and m are each, independently of one another, from 1 to 6. Preferably, m=1 and n is from 1 to 4.
Through a suitable choice of the meanings of R1 to R13, the addressing times, the threshold voltage, the steepness of the transmission characteristic lines, etc., can be modified in the desired manner. For example, 1E-alkenyl radicals, 3E-alkenyl radicals, 2E-alkenyloxy radicals and the like generally result in shorter addressing times, improved nematic tendencies and a higher ratio of the elastic constants k33 (bend) and k11 (splay) compared with alkyl and alkoxy radicals. 4-alkenyl radicals, 3-alkenyl radicals and the like generally give lower threshold voltages and smaller values of k33/k11 compared with alkyl and alkoxy radicals.
The optimum mixing ratio of the compounds of the formulae I-VI depends substantially on the desired properties, on the choice of the components of the formulae I, II, III, IV, V and/or VI and on the choice of any further components present. Suitable mixing ratios within the range indicated above can easily be determined from case to case.
The total amount of compounds of the formulae I to VI in the mixtures according to the invention is not crucial. The mixtures preferably consist of 50-90% by weight of compounds of the formulae I to VI. The mixtures may also comprise one or more further components in order to optimize various properties. However, the observed effect, particularly on the low-temperature stability, is generally greater the higher the total concentration of compounds of the formulae I to VI.
The liquid-crystalline media according to the invention preferably comprise from 2 to 40, in particular from 4 to 30, compounds as further constituents besides one or more compounds of the formula I. These media very particularly preferably comprise from 7 to 25 compounds besides one or more compounds of the formula I. These further constituents are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular substances from the classes of the azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl esters of cyclohexanecarboxylic acid, phenyl or cyclohexyl esters of cyclohexylbenzoic acid, phenyl or cyclohexyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters of benzoic acid, of cyclohexanecarboxylic acid or of cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4xe2x80x2-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes, 1-phenyl-2-cyclohexylethanes, 1-cyclohexyl-2-(4-phenylcyclohexyl)ethanes, 1-cyclohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexylphenylethanes, optionally halogenated stilbenes, benzyl phenyl ethers, tolans and substituted cinnamic acids. The 1,4-phenylene groups in these compounds may also be fluorinated.
The most important compounds suitable as further constituents of media according to the invention can be characterized by the formulae 1, 2, 3, 4 and 5:
Rxe2x80x2xe2x80x94Lxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x831
Rxe2x80x2xe2x80x94Lxe2x80x94COOxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x832
Rxe2x80x2xe2x80x94Lxe2x80x94OOCxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x833
Rxe2x80x2xe2x80x94Lxe2x80x94CH2CH2xe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x834
Rxe2x80x2xe2x80x94Lxe2x80x94Cxe2x89xa1Cxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x835
In the formulae 1, 2, 3, 4 and 5, L and E, which may be identical or different, are each, independently of one another, a bivalent radical from the group formed by -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- and their mirror images, where Phe is unsubstituted or fluorine-substituted 1,4-phenylene, Cyc is trans-1,4-cyclohexylene or 1,4-cyclohexylene, Pyr is pyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio is 1,3-dioxane-2,5-diyl, and G is 2-(trans-1,4-cyclohexyl)ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.
One of the radicals L and E is preferably Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. The media according to the invention preferably comprise one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which L and E are selected from the group consisting of Cyc, Phe and Pyr and simultaneously one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which one of the radicals L and E is selected from the group consisting of Cyc, Phe and Pyr and the other radical is selected from the group consisting of -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-, and optionally one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which the radicals L and E are selected from the group consisting of -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-.
In a smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, Rxe2x80x2 and Rxe2x80x3 are each, independently of one another, alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8 carbon atoms. This smaller sub-group is called Group A below, and the compounds are referred to by the sub-formulae 1a, 2a, 3a, 4a and 5a. In most of these compounds, Rxe2x80x2 and Rxe2x80x3 are different from one another, one of these radicals usually being alkyl, alkenyl, alkoxy or alkoxyalkyl.
In another smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, which is known as Group B, Rxe2x80x3 is xe2x80x94F, xe2x80x94Cl, xe2x80x94NCS or xe2x80x94(O)iCH3xe2x88x92(k+l)FkCll, where i is 0 or 1, and k+l is 1, 2 or 3; the compounds in which Rxe2x80x3 has this meaning are referred to by the sub-formulae 1b, 2b, 3b, 4b and 5b. Particular preference is given to those compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b in which Rxe2x80x3 is xe2x80x94F, xe2x80x94Cl, xe2x80x94NCS, xe2x80x94CF3, xe2x80x94OCHF2 or xe2x80x94OCF3.
In the compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b, Rxe2x80x2 is as defined for the compounds of the sub-formulae 1a-5a and is preferably alkyl, alkenyl, alkoxy or alkoxyalkyl.
In a further smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, Rxe2x80x3 is xe2x80x94CN; this sub-group is referred to below as Group C, and the compounds of this sub-group are correspondingly described by sub-formulae 1c, 2c, 3c, 4c and 5c. In the compounds of the sub-formulae 1c, 2c, 3c, 4c and 5c, Rxe2x80x2 is as defined for the compounds of the sub-formulae 1a-5a and is preferably alkyl, alkoxy or alkenyl.
Besides the preferred compounds of groups A, B and C, other compounds of the formulae 1, 2, 3, 4 and 5 having other variants of the proposed substituents are also customary. All these substances are obtainable by methods which are known from the literature or analogously thereto.
Besides the compounds of the formula I to VI, the media according to the invention preferably comprise one or more compounds selected from Group A and/or Group B and/or Group C. The proportions by weight of the compounds from these groups in the media according to the invention are preferably
Group A: from 0 to 90%, preferably from 20 to 90%, in particular from 30 to 90%
Group B: from 0 to 80%, preferably from 10 to 80%, in particular from 10 to 65%
Group C: from 0 to 80%, preferably from 5 to 80%, in particular from 5 to 50%,
the sum of the proportions by weight of the Group A and/or B and/or C compounds present in the respective media according to the invention preferably being from 5% to 90% and in particular from 10% to 90%.
The structure of the IPS display according to the invention corresponds to the usual design for displays of this type, as described, for example, in WO 91/10936 or EP 0 588 568. The term usual design is broadly drawn here and also covers all derivatives and modifications of the IPS display, in particular, for example, also matrix display elements based on poly-Si TFT or MIM.
However, an essential difference of the displays according to the invention from those usual hitherto consists in the choice of the liquid-crystal parameters of the liquid-crystal layer.
The liquid-crystal mixtures which can be used in accordance with the invention are prepared in a manner conventional per se. In general, the desired amount of the components used in smaller amount is dissolved in the components making up the principal constituent, advantageously at elevated temperature. It is also possible to prepare the mixtures in other conventional manners, for example by use of premixtures, for example homologue mixtures, or using so-called xe2x80x9cmultibottlexe2x80x9d systems.
The dielectrics may also comprise further additives known to the person skilled in the art and described in the literature. For example, 0-15%, preferably 0-10%, of pleochroic dyes and/or chiral dopants may be added.
The individual compounds added are employed in concentrations of from 0.01 to 6% and preferably from 0.1 to 3%. However, the concentrations given here for the other constituents of the liquid-crystal mixtures, i.e. the liquid-crystalline or mesogenic compounds, are indicated without taking into account the concentration of these additives.
Above and below, 
denote trans 1,4-cyclohexylene.
The physical properties of the liquid-crystal mixtures are determined in accordance with xe2x80x9cPhysical Properties of Liquid Crystalsxe2x80x9d Ed. M. Becker, Merck KGaA, as of November 1997, unless explicitly stated otherwise.
C denotes a crystalline phase, S a smectic phase, SC a smectic C phase, SA a smectic A phase, N a nematic phase and I the isotropic phase. V0 denotes the capacitive threshold voltage. xcex94n denotes the optical anisotropy, and n0 the ordinary refractive index (in each case at 589 nm). xcex94xcex5 denotes the dielectric anisotropy (xcex94xcex5=xcex5∥xe2x88x92xcex5xe2x8axa5, where xcex5∥ denotes the dielectric constant parallel to the longitudinal molecular axes and xcex5xe2x8axa5 denotes the dielectric constant perpendicular thereto, in each case at 1 kHz). The electro-optical data were measured in a planar cell at 20xc2x0 C., unless expressly stated otherwise. All physical properties are indicated and measured at 20xc2x0 C., unless expressly stated otherwise.
The cells are preferably bright in the xe2x80x9coffxe2x80x9d state.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
In the foregoing and in the following examples, all temperatures are set forth uncorrected in degrees Celsius, and, unless otherwise indicated, all parts and percentages are by weight.
The entire disclosure of all applications, patents and publications, cited above or below, and of corresponding German Application No. DE 100 17 385.3 filed Apr. 7, 2000, is hereby incorporated by reference.
xcex94n denotes optical anisotropy (589 nm, 20xc2x0 C.), xcex94xcex5 denotes the dielectric anisotropy (1 kHz, 20xc2x0 C.), H.R. denotes the voltage holding ratio (at 100xc2x0 C., after 5 minutes in an oven at 1 V), and V0, the capacitive threshold voltage, was determined at 20xc2x0 C. and 1 kHz.
The calibrated rotational viscometer gave a rotational viscosity xcex31 for ZLI-4792 (Merck KGaA) of 133 mPaxc2x7s at 20xc2x0 C.
The shelf life was investigated in sealed test cells with an optical retardation of about 0.5 xcexcm with CU-1511 from DuPont, USA, as alignment layer. To this end, in each case five test cells were bonded on both sides to crossed polarizers and stored at fixed temperatures of 0xc2x0 C., xe2x88x9210xc2x0 C., xe2x88x9220xc2x0 C., xe2x88x9230xc2x0 C. and xe2x88x9240xc2x0 C. At intervals of 24 hours in each case, the cells were assessed visually for changes. The storage time noted at the respective temperature tstore (T) was the final time at which a change was just not observed in any cell.
In the present application and in the examples below, the structures of the liquid-crystal compounds are indicated by means of acronyms, the transformation into chemical formulae taking place in accordance with Tables A and B below. All radicals CnH2n+1 are straight-chain alkyl radicals having n carbon atoms. The coding in Table B is self-evident. In Table A, only the acronym for the parent structure is indicated, followed in individual cases, separated from the acronym for the parent structure by a dash, by a code for the substituents R1, R2, L1 and L2:
Preferred displays contain media comprising, in particular, one or more compounds from Tables A and B in addition to the compounds of the formula I.
Particularly preferred IPS displays contain media comprising
one or more compounds of one of the formulae from Table A and one or more compounds of the formulae from Table B
in each case one or more compounds of two or more different types of compounds of the formulae from Table A
in each case one or more compounds of two or more different types of compounds of the formulae from Table B
in each case one or more compounds of four or more compounds from the group consisting of the compounds of the formulae from Tables A and B.